Researchers at EPFL and the Swiss Federal Office of Food Safety have identified several rubber-related chemicals in Swiss raw milk. The study also suggests that dairy equipment may be an overlooked source of contamination.
Every year, tire and road wear release an estimated six million tons of rubber particles into the environment, some of which eventually reach agricultural land through the air, water runoff and fertilizers. Because dairy farms often operate near roads, rubber-related chemicals can make their way into milk, potentially exposing humans.
To investigate whether these compounds are present in Swiss dairy production, a team from EPFL led by Florian Breider, director of the EPFL Central Environmental Laboratory, and the Federal Food Safety and Veterinary Office (FSVO) in collaboration with Agroscope, analyzed the composition of milk samples from 17 different Swiss farms.
The analysis revealed four rubber-related chemicals in raw milk, and at least one of these compounds was present in seven of the 17 samples analyzed. In contrast, none of the target compounds were detected in the three samples collected from alpine farms located far from busy roads. However, the sample size was too small to establish a clear relationship between contaminant concentrations and road traffic near the farms.
More surprising was the discovery that dairy equipment itself may contribute to contamination. Indeed, analysis of hoses, seals and other rubber components used in milk production revealed 14 rubber-related chemicals. "What is surprising is that these compounds come from materials legally authorized to be in contact with food," says Breider.
The results, published in Food Chemistry X, show that although concentrations found were generally low, we need to better understand the pathway these chemical follows before they reach milk and to assess any potential risks to public health. "This work was a preliminary study, and we need to evaluate the actual risks associated with these findings," says Breider.
An unexpected potential source
During collection and processing, milk passes through equipment which components are made of rubber-based materials that contain additives. These additives make materials more flexible, resistant to heat and wear, and better able to withstand repeated use. However, over time, these rubbers and additives may gradually release small amounts of the chemicals they contain, a process known as migration, representing a potential pathway through which rubber-related chemicals could enter the food supply.
Researchers analyzed the composition of different rubber-based materials and dairy equipment present in farms that already presented some level of degradation. Among 14 other compounds detected in the materials analyzed, researchers found a compound called 6PPD-quinone (6PPD-Q), known to be harmful to certain fish species. This molecule is not intentionally added to tires or other rubber products. Instead, it forms over time after the oxidation of rubber additives as materials age.
The findings suggest that the design and composition of some materials used in food production may require closer examination to avoid the contamination of dairy products. According to Breider, "Before regulating, we should conduct more studies to evaluate to what extent this impacts also other types of industries."
Health impact to be determined
While the implications for human health remain unknown, the findings point to the need for further research into how rubber-related chemicals enter food production systems and whether long-term dietary exposure poses any risks. The work also raises broader questions about the materials used throughout modern food supply chains.
Researchers now aim to obtain a more detailed picture by monitoring how the concentrations of these chemical compounds change from season to season and performing migration studies under realistic milking conditions. Targeted risk assessments would help understand the precise origin of the rubber-related compounds that can support the development of safer materials for food-contact applications.
